1. Field of the Invention
The present invention relates to an insulating layer, a semiconductor device and methods for fabricating the same, and more particularly, to an insulating layer, a semiconductor device and methods for fabricating the same that includes a borophosphosilicateglass (BPSG) layer to control the additive amounts of boron (B) and phosphorous (P) most efficiently.
2. Description of the Related Art
Semiconductor devices require high capacity and fast operating speeds to power today""s electronic devices. Accordingly, semiconductor device manufacturing methods continually strive to improve the integration density, reliability, and response times of the devices. As one example, consider the DRAM memory class, where 16M and 64M devices are being mass produced, 256M devices are starting to be mass produced, and plans for mass production of 1G devices are being explored.
Critical techniques to improve the integration density of semiconductor devices include layer fabricating techniques for insulating and conductive layers. The layer fabricating techniques can largely be classified into physical vapor deposition and chemical vapor deposition. The chemical vapor deposition technique provides a gas source, which includes supplying an element of an object material to be formed, and a reaction gas onto a substrate, and then forms a layer on the substrate by heating the substrate to initiate a chemical reaction.
As the semiconductor devices become more advanced, the parameters and requirements for the processing techniques to form a layer used for fabricating a semiconductor device are becoming more rigorous. This is because the insulating layers and conducting layers are formed in a multi-layer structure, and those layers have to be formed in a fine pattern with a design rule of 0.15 xcexcm or less.
When those layers are formed to have the fine patterns, the process characteristics for making the fine pattern affect not only the layer on which the fine pattern is formed, but also the underlying and upper layers. Therefore, when the layers are formed, the chemical and physical characteristics of the other layers must be considered when deciding on the process characteristics of the layer to be formed.
A phosphosilicateglass (PSG) layer, which dopes phosphorus into an oxidized material, or a BPSG layer, which dopes boron and phosphorus into an oxidized material, are the primary layer types used for an insulating layer to protect a surface or to electrically isolate a metal wire. This is mainly due to the excellent step coverage of the PSG layer or the BPSG layer. Also, the PSG or BPSG layers getter alkali ion while reacting as a diffusion wall against humidity, and the processes for forming the layers can easily be performed in a low temperature regime.
However, there is a disadvantage to using PSG or BPSG layers. Since these layers have enough fluidity and create a diffusion wall during a reflow process, the layers also operate as an intermediary to pass on the humidity to the underlying layers. Accordingly, in a case where a layer is composed of a material that can be damaged by humidity, or an underlying substrate is made of silicon, it may cause a serious problem. Therefore, a method to minimize the influence of the humidity has to be fully considered when the PSG and BPSG layers are being formed.
Examples for forming PSG and BPSG insulating layers are disclosed in U.S. Pat. No. 4,668,973 (issued to Dawson et al.), Japanese Patent Laid-Open No. Sho 59-22945, Japanese Patent Laid-Open No. Hei 1-122139, and Japanese patent Laid-Open No. Hei 8-17926.
In U.S. Pat. No. 4,668,973, the PSG layer is formed by adding 7% or less of phosphorus into a nitride silicon layer after forming the nitride silicon layer on the substrate. Accordingly, the nitride silicon layer prevents the humidity from penetrating into the substrate even though the PSG layer has been reflowed. Furthermore, even if a window is formed at the PSG layer, since the substrate is not directly exposed by means of the nitride silicon layer, the substrate may be prevented from being oxidized.
In Japanese Patent Laid-Open No. Sho 59-222945, a nitride silicon layer is formed on a substrate and then a BPSG layer is formed on the nitride silicon layer. The nitride silicon layer prevents the humidity from penetrating into the substrate even though the BPSG layer has been reflowed. Therefore, it is able to prevent the substrate from being oxidizing by direct exposure.
In Japanese Patent Laid-Open No. Hei 1-122139, a nitride silicon layer is successively formed on the substrate and a gate electrode and thereafter a BPSG layer containing boron is formed. Therefore, the nitride silicon layer prevents the humidity from penetrating into the substrate or the gate electrode even though the BPSG layer has been reflowed.
In Japanese Patent Laid-Open No. Hei 8-17926, an oxide silicon layer is formed onto a polysilicon layer and then the BPSG layer is formed onto the oxide silicon layer. Therefore, the oxide silicon layer prevents the humidity from penetrating into the polysilicon layer or the substrate even if the BPSG layer has been reflowed.
In this way, when forming the insulating layer including the PSG layer or BPSG layer, the effect of the humidity can be minimized by means of forming the PSG layer or BPSG layer on the underlying nitride silicon layer. Also, the nitride silicon layer prevents the underlying layer or the substrate from being damaged by means of etching, for example, when a portion of the insulating layer is patterned and etched to form a window.
In the present fabricating method for a semiconductor device having elevated regions and recessed regions composed of minute windows or gate electrodes, one must consider the need to sufficiently force or charge the BPSG insulating layer into the recessed regions of the windows or the gate electrodes. Therefore, a chemical vapor deposition using a tetraethylorthosilicate (TEOS), a triethylborate (TEB), a triethylphosphate (TEPO), an oxygen gas and an ozone gas is employed to form the BPSG layer.
The BPSG layer is formed as follows. First, an oxidizing atmosphere for easily forming the BPSG layer is prepared using oxygen gas. After forming a first seed layer onto an etch stop layer comprising the nitride silicon layer using the TEOS and the oxygen gas, a second seed layer is formed onto the first seed layer using the triethylborate (TEB), the triethylphosphate (TEPO), the tetraethylorthosilicate (TEOS) and the oxygen gas. The constituents of the first and second seed layers determine the amount of boron and phosphorous added into the BPSG layer. Subsequently, the BPSG layer is formed onto the etch stop layer including the first and the second seed layers by using the triethylborate, the triethylphosphate, the tetraethylorthosilicate and the ozone gas. With this method, the BPSG layer is formed with a relatively large amount of phosphorous because the triethylphosphate is used to form the second seed layer.
While the BPSG layer has sufficient fluidity for normal circumstances, in a subsequent reflow process with nitrogen gas, the BPSG layer is not fully charged or filled into the recessed regions voids are frequently generated.
Therefore, oxygen gas and hydrogen gas are sometimes used instead of nitrogen gas to reflow the BPSG layer to minimize the generation of voids. However, when the BPSG layer has been reflowed with the oxygen gas and the hydrogen gas, the thickness of the etch stop layer under the BPSG layer is decreased. This is because phosphoric acid H3PO4 is generated by a chemical reaction between the triethylphosphate, which determines the amount of phosphorus, and the oxygen gas and the hydrogen gas, which acid etches the etch stop layer while reflowing progresses.
Indeed, the thickness of the etch stop layer decreased by about 30% after reflowing with oxygen/hydrogen according to an analyzed result of the etch stop layer before and after the reflow with a transmission electron microscope (TEM). Also, using auger electron spectroscopy (AES), it was seen that the oxidized materials composing the etch stop layer after reflowing have been increased about 0.2 times more than before reflowing. This confirms that the thickness of the etch stop layer is decreased by the reflowing process and the oxidization is progressing thereby.
Given the above, the etch stop layer is unable to appropriately control the etching process when the BPSG layer is etched to form a BPSG layer pattern having a window after the reflowing. Consequently, the substrate under the etch stop layer is exposed, or even the substrate itself is etched. In a semiconductor device fabricating process which requires a fine pattern such as a self-aligned contact, the decrease in thickness of the etch stop layer precludes attaining a sufficient shoulder margin between the gate electrodes.
Even when using a BPSG layer containing a relatively large amount of the boron, rather than the PSG layer containing a relatively large amount of the phosphorous, the BPSG layer is not charged into the recessed region and voids are created because the BPSG layer does not have sufficient fluidity. Also, since the BPSG layer has an isotropic etch characteristic, the etched window that is formed is larger than a predetermined critical dimension CD. Therefore, in the subsequent process for charging the window, the inside portion of the window is not sufficiently charged and a void is generated. Accordingly, when the layer for charging the window is made of a metal, the void may cause a bridge.
As described above, since the amount of the phosphorous and the boron added to the BPSG layer is not controlled, the thickness of the underlying etch stop layer decreases or the etch stop layer has the isotropic etch characteristic, whereby the reliability of the semiconductor device fabricating method is reduced.
Therefore, it is an object of the present invention to provide an insulating layer including a BPSG layer capable of optimizing the amount of boron and phosphorous without a changing the characteristics of the layer.
It is another object of the present invention to provide a method for forming an insulating layer including a BPSG layer capable of optimizing the amount of the boron and phosphorous without changing the characteristics of the layer.
It is still another object of the present invention to provide a semiconductor device including an insulating layer constituted of a BPSG layer capable of optimizing the amount of boron and phosphorous without changing the characteristics of the layer.
To achieve the aforementioned object, the present invention includes an insulating layer of a semiconductor device comprising a BPSG layer, in which about 5.25-5.75% by weight of boron and about 2.75-4.25% by weight of phosphorus are added to a tetraethylorthosilicate.
To achieve another object of the present invention, there is provided a method for forming an insulating layer including steps of preparing an oxidizing atmosphere to form the insulating layer on a substrate by using an oxygen gas, forming a first seed layer of the insulating layer on the substrate by using a tetraethylorthosilicate and an oxygen gas, forming a second seed layer of the insulating layer capable of controlling an amount of a boron added to the first seed layer by using a triethylborate, the tetraethylorthosilicate and the oxygen gas, and forming a BPSG layer capable of controlling the amount of the boron and a phosphorus added to the insulating layer having the first seed layer and second seed layer by using the triethylborate, triethylphosphate, the tetraethylorthosilicate and an ozone gas.
The insulating layer can be formed as follows. After preparing the oxidizing atmosphere, the first seed layer is formed by providing the tetraethylorthosilicate and the oxygen gas with a mixed ratio of 1:5.4 to 5.8, and the second seed layer is formed by providing the tetraethylorthosilicate, the triethylborate and the oxygen gas with a mixed ratio of 1:0.2 to 0.3:5.4 to 5.8. Next, the BPSG layer is formed onto the first seed layer and the second seed layer by providing the tetraethylorthosilicate, the triethylborate, the triethylphosphate and the ozone gas with a mixed ratio of 1:0.2 to 0.3:0.09 to 0.12:5.4 to 5.8. The insulating layer is formed under a reduced pressure (which is close to a vacuum environment) in an atmosphere of helium gas and a nitrogen gas with a mixed ratio of 1:1.8 to 2.2.
The etch stop layer on the substrate consists of a nitride silicon layer to prevent the substrate from being damaged by etching when the insulating layer is etched. The insulating layer is reflowed with hydrogen and oxygen gas to evenly form the upper surface of the insulating layer and simultaneously charge the recessed regions among the elevated regions and the recessed regions at the surface of the substrate.
Even though the insulating layer has been reflowed by the oxygen gas and the hydrogen gas, the etch stop layer prevents the substrate from being damaged, so that an isotropic etch characteristic can be reduced. As a result, the recessed regions can be fully charged and simultaneously the insulating layer can be etched in an anisotropic etch. Accordingly, the inventive insulating layer having the BPSG layer can be appropriately adopted to form a self-aligned contact and a fine pattern.
To achieve still another object of the present invention, there is provided a semiconductor device including a substrate having a gate electrode formed at an upper portion of the substrate, a source and a drain formed at a lower portion of both sides of the gate electrode, and an insulating layer to which about 5.25-5.75% by weight of boron and about 2.75-4.25% by weight of phosphorus is added, where the insulating layer is continuously formed on the substrate and the gate electrode.
To achieve yet another object of the present invention, there is provided a method for fabricating a semiconductor device including the steps of forming an etch stop layer on a substrate for preventing the substrate from being damaged by etching, forming an insulating layer, to which about 5.25-5.75% by weight of boron and about 2.75-4.25% by weight of phosphorus is added, on the etch stop layer, reflowing the insulating layer to evenly form an upper surface of the insulating layer and simultaneously charge recessed regions with the insulating layer among elevated regions and recessed regions of the substrate, and etching a predetermined portion of the insulating layer to form an insulating layer pattern having a window which exposes the surface of the underlying etch stop layer.
The substrate has elevated regions and recessed regions and the elevated regions and the recessed regions are formed by the gate electrodes and the patterns having the window.
The etch stop layer is formed to have a thickness of about 60 to 140 xc3x85 by using a nitride silicon gas and the insulating layer is formed to have a thickness of about 9,000 to 10,000 xc3x85. The etch stop layer and the insulating layer are formed by means of a chemical vapor deposition.
Accordingly, the recessed regions can be sufficiently charged and simultaneously the insulating layer can be etched by an anisotropic etch. By controlling the amount of added phosphorus and boron most efficiently, the etch stop layer prevents the substrate from being etched even though the insulating layer having the BPSG layer has been reflowed and the isotropic etch characteristic is reduced. Therefore, the insulating layer having the BPSG layer can be appropriately adopted for the self-aligned contact which requires the design rule of 0.15 um or less or for forming fine patterns.